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@ARTICLE{Schlter:21588,
      author       = {Schlüter, S. and Vanderborght, J. and Vogel, H.-J.},
      title        = {{H}ydraulic non-equilibrium during infiltration induced by
                      structural connectivity},
      journal      = {Advances in water resources},
      volume       = {44},
      issn         = {0309-1708},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {PreJuSER-21588},
      pages        = {101 - 112},
      year         = {2012},
      note         = {The first author has been financially supported by
                      Helmholtz Association through the Virtual Institute INVEST
                      (Inverse Modelling of Terrestrial Systems) and has been
                      kindly supported by Helmholtz Impulse and Networking Fund
                      through Helmholtz Interdisciplinary Graduate School for
                      Environmental Research (HI-GRADE). We thank Max Kohne, Uli
                      Weller and Gerrit de Rooij for fruitful discussions and four
                      anonymous reviewers for their valuable comments.},
      abstract     = {Water infiltration into heterogeneous, structured soil
                      leads to hydraulic non-equilibrium across the infiltration
                      front. That is, the water content and pressure head are not
                      in equilibrium according to some static water retention
                      curve. The water content increases more rapidly in more
                      conductive regions followed by a slow relaxation towards an
                      equilibrium state behind the front. An extreme case is
                      preferential infiltration into macropores.Since flow paths
                      adapt to the structural heterogeneity of the porous medium,
                      there is a direct link between structure and
                      non-equilibrium. The aim of our study is to develop an
                      upscaled description of water dynamics which conserves the
                      macroscopic effects of non-equilibrium and which can be
                      directly linked to structural properties of the material. A
                      critical question is how to define averaged state variables
                      at the larger scale. We propose a novel approach based on
                      flux-weighted averaging of pressure head, and compare its
                      performance to alternative methods for averaging. Further,
                      we suggest some meaningful indicators of hydraulic
                      non-equilibrium that can be related to morphological
                      characteristics of infiltration fronts in quantitative
                      terms. These methods provide a sound basis to assess the
                      impact of structural connectivity on hydraulic
                      non-equilibrium.We demonstrate our approach using numerical
                      case studies for infiltration into two-dimensional
                      heterogeneous media using three different structure models
                      with distinct differences in connectivity. Our results
                      indicate that an increased isotropic, short-range
                      connectivity reduces non-equilibrium, whereas anisotropic
                      structures that are elongated in the direction of flow
                      enforce it. We observe a good agreement between front
                      morphology and effective hydraulic non-equilibrium. A
                      detailed comparison of averaged state variables with results
                      from an upscaled model that includes hydraulic
                      non-equilibrium outlines potential improvements in the
                      description of non-equilibrium dynamics including
                      preferential flow in simplified, upscaled models based on
                      Richards equation. (C) 2012 Elsevier Ltd. All rights
                      reserved.},
      keywords     = {J (WoSType)},
      cin          = {IBG-3},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {Terrestrische Umwelt},
      pid          = {G:(DE-Juel1)FUEK407},
      shelfmark    = {Water Resources},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000306615700007},
      doi          = {10.1016/j.advwatres.2012.05.002},
      url          = {https://juser.fz-juelich.de/record/21588},
}